Concretes are solid materials formed by combining aggregate particles with a mortar-like paste to form a slurry. Commonly, the mortar-like paste comprises a mixture of cement, such as Portland cement, water, and, optionally, a pozzolonic material. The cement reacts chemically with the water to form a solid material.
It is known in the art that polymers, in liquid form, can be added to cementitious slurries to absorb excess water in the mixture and/or to enhance the properties of the composite materials. It is further known to use polymeric cementitious compositions to make high compressive strength concretes, such as with strengths between about 10,000 and about 30,000 psi. Also, it is known to make highly adhesive concretes, but these generally are expensive and difficult to work with because they set very quickly and are heat sensitive.
Heretofore, the mixing of polyacrylamide polymers into a cementitious slurry has been thought to be possible only in liquid form and then only in conjunction with an aqueous foamed surfactant. To mix a polyacrylamide polymer uniformly into a cementitious slurry, the polymer is added in liquid, diluted form along with a foaming surfactant, followed by foaming the slurry with high pressure compressed air. The foaming step is considered necessary to ensure complete mixing of the component materials into a homogeneous, flowable material which is then poured into a space to be filled and allowed to set. These conventional processes require high pressure foam generating equipment and adroit operators who are able to recognize and respond appropriately to changes in the foam generator output. Visual interpretation of the equipment's operating condition is a subjective art, and the quality of the finished product is highly dependent upon the skill level of the workmen.
Relatively low compressive strength concretes, known as "flow-fill", are commonly used in a variety of applications, such as backfill for bridge abutments and retaining walls, trench backfill for utility and underground cable and pipe line, and subsidence backfill. In other applications, it is desirable to allow fluids to move through the concrete. These fluids, including suspended solids and gases, can either be collected for further processing, or they can be discharged into soil water, or the atmosphere for dispersal. Pervious concrete can be utilized in construction applications, either alone or in conjunction with drainage pipes, to direct water away from a structure or road surface, thereby reducing the potential for damage by erosion, chemical action, or hydraulic pressure.
Conventional cementitious slurries used to make low-strength composite materials generally contain more water than is required to react with the cement. This excess water reduces the slurry viscosity and renders the slurry flowable. These conventional materials commonly settle 5-6 percent or more due to liquid-solid separation before and during setting of the cementitious slurry, resulting in bleeding of excess water from the top and a nonhomogeneous, layered concrete material. Thus, it is often necessary to pour the backfill in stages, known in the art as "lifts", requiring substantial labor and accompanying costs. Further settling and/or compaction after the material sets can cause subsequent problems. For example, settling of bridge abutments can cause bumps and ridges in the overlying roadway at the junction between the abutment and the bridge.
A further disadvantage of conventional low-strength cementitious materials is that excess water can become entrapped in the composite material and/or the adhesive if it is not adequately pervious and/or if the water cannot drain freely from the material. Also, conventional cementitious adhesives are at least somewhat permeable to water. Thus, water, such as might be present from the formation of the composite or due to rain or melting snow, can penetrate the adhesive and migrate in a capillary manner to the interface between the coating and the aggregate. Further, the finished product also contains surfactant, which may enhance the water permeability of the cementitious adhesive by reducing the surface tension necessary to overcome capillary forces. Thus, water entrapped either in hydraulically isolated pore spaces between adhesive-coated aggregate particles, within the adhesive, or at the aggregate/adhesive interface can cause significant spalling and structural damage during repeated cycles of freezing and thawing.
Thus, there is a need for a surfactant-free cementitious adhesive which can be used to prepare relatively low-strength composite materials which are pervious, homogeneous, self-draining, non-shrinking, non-bleeding, and resistant to freeze/thaw damage. There is also a need for a surfactant-free cementitious composite material which is adhesive, pervious, self-draining, non-shrinking, non-bleeding, and resistant to freeze/thaw damage. There is a further need for a simpler, cost-effective method of making cementitious composite materials which does not require the use of surfactants and foam generating equipment. There is yet a further need for a cementitious composition which sets slowly enough to make it easy to emplace and work with. There is an additional need for a low-strength cementitious composite material which can be emplaced in a single stage, without multiple lifts.